/*
 * Copyright 2011 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.glagol.sourcemap;

import java.util.Arrays;

/**
 * A utility class for working with Base64 values.
 * @author johnlenz@google.com (John Lenz)
 */
public final class Base64 {

    // This is a utility class
    private Base64() {}

    /**
     *  A map used to convert integer values in the range 0-63 to their base64
     *  values.
     */
    private static final String BASE64_MAP =
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
                    "abcdefghijklmnopqrstuvwxyz" +
                    "0123456789+/";

    /**
     * A map used to convert base64 character into integer values.
     */
    private static final int[] BASE64_DECODE_MAP = new int[256];
    static {
        Arrays.fill(BASE64_DECODE_MAP, -1);
        for (int i = 0; i < BASE64_MAP.length(); i++) {
            BASE64_DECODE_MAP[BASE64_MAP.charAt(i)] = i;
        }
    }

    /**
     * @param value A value in the range of 0-63.
     * @return a base64 digit.
     */
    public static char toBase64(int value) {
        assert (value <= 63 && value >= 0) : "value out of range:" + value;
        return BASE64_MAP.charAt(value);
    }

    /**
     * @param c A base64 digit.
     * @return A value in the range of 0-63.
     */
    public static int fromBase64(char c) {
        int result = BASE64_DECODE_MAP[c];
        assert (result != -1) : "invalid char";
        return result;
    }

    /**
     * @param value an integer to base64 encode.
     * @return the six digit long base64 encoded value of the integer.
     */
    public static String base64EncodeInt(int value) {
        char[] c = new char[6];
        for (int i = 0; i < 5; i++) {
            c[i] = Base64.toBase64((value >> (26 - i * 6)) & 0x3f);
        }
        c[5] = Base64.toBase64((value << 4) & 0x3f);
        return new String(c);
    }
}